Recently, short-wavelength semiconductor lasers have been intensively developed for the application of the semiconductor lasers in high density optical disk recording and the like. Hexagonal compound semiconductors including nitrogen (hereinafter, simply called nitride semiconductors) such as GaN, AlGaN, InGaN, InGaAlN and GaPN are used for short wavelength semiconductor lasers. In addition, LEDs using nitride semiconductors also have been developed.
As the nitride semiconductor light emitting elements, light emitting elements of the MIS structure have been used in some cases. However, such a light emitting element has a high-resistance i-type GaN-based semiconductor stacked thereon, and accordingly has a problem of generally very low emission output. To solve such a problem, the i-type GaN-based semiconductor layer is irradiated with electrons or is annealed.
Additionally, even for a nitride semiconductor light emitting element having a p-type GaN-based semiconductor layer formed therein, efforts are made to increase the emission output. For example, in order to improve the luminous efficiency, it is proposed, as disclosed in Patent Document 1, that the forward voltage Vf be reduced by forming an ohmic contact between a p-electrode and a p-type GaN contact layer or by making smaller the film thickness of a p-type GaN contact layer.
Moreover, in order to improve the luminous efficiency, Patent Document 1 also proposes that Mg be used as a p-type dopant to obtain the p-type characteristics of a p-type AlGaN cladding layer, or that the film thickness and the Al composition of the p-type AlGaN cladding layer be specified to improve the crystallinity.    Patent Document 1: Japanese Patent No. 2778405